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How To Make Invisible Ink - Baking Soda

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This smiley face was made with invisible ink. The face became visible when the paper was heated.

This smiley face was made with invisible ink. The face became visible when the paper was heated.

Anne Helmenstine

These are instructions for making non-toxic invisible ink using baking soda (sodium bicarbonate).

Difficulty: Easy

Time Required: A Few Minutes

Here's How:

  1. There are at least two methods to use baking soda as an invisible ink. Mix equal parts water and baking soda.
  2. Use a cotton swab, toothpick, or paintbrush to write a message onto white paper, using the baking soda solution as 'ink'.
  3. Allow the ink to dry.
  4. One way to read the message is to hold the paper up to a heat source, such as a light bulb. The baking soda will cause the writing in the paper to turn brown.
  5. A second method to read the message is to paint over the paper with purple grape juice. The message will appear in a different color.

Tips:

  1. If you are using the heating method, avoid igniting the paper - don't use a halogen bulb.
  2. Baking soda and grape juice react with each other in an acid-base reaction, producing a color change in the paper.
  3. The baking soda mixture can also be used more diluted, with one part baking soda to two parts water.
  4. Grape juice concentrate results in a more visible color change than regular grape juice.

What You Need:

  • Baking Soda
  • Paper
  • Water
  • Light Bulb (heat source)
  • Paintbrush or Swab
  • Measuring Cup
  • Purple Grape Juice (opt.)

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